Google App Engine: an introduction to its data warehouse API for people with SQL background?

Question

Does anyone have any good information besides Google App Engine documents provided by Google that provide a good overview for people with an MS SQL database to port their knowledge and use the Google App Engine datastore API effectively.

For example, if you have your own user table and message table

Where is the relationship between users and the message (associated with UserID), how will this structure be displayed in Google App Engine?

SELECT * FROM Users INNER JOIN Message ON Users.ID = Message.UserID 

Answer 1

Here is a good link: one to many join using the Google App Engine.

http://blog.arbingersys.com/2008/04/google-app-engine-one-to-many-join.html

Here is another good link: many of the many join with the Google App Engine:

http://blog.arbingersys.com/2008/04/google-app-engine-many-to-many-join.html

Here is a good discussion of two links:

http://groups.google.com/group/google-appengine/browse_thread/thread/e9464ceb131c726f/6aeae1e390038592?pli=1

Personally, I find this comment in the discussion very informative in the Google App Engine datastore:

http://groups.google.com/group/google-appengine/msg/ee3bd373bd31e2c7

On a scale, you are shutting down things that seem wrong, but these are the required numbers, we are running. Go see the EBay talks. Or read the messages about how many database instances of FaceBook are running.

The simple truth is that what we learned about in uni is great for an application for automating a business from small to medium-sized applications, where the load was predictable, and there was enough money to buy a server, it takes 50 people to enter the data to process the data, billing or business planning and management application ....

I searched a bit more and came across this Google Doc article:

http://code.google.com/appengine/articles/modeling.html

App Engine allows you to create simple-to-use relationships between data warehouse entities that can represent real things and ideas. using ReferenceProperty when you need to match an arbitrary number of repeating kinds of information with a single object. Use key lists when you need to allow many different objects to exchange other instances between each other. You will find that these two approaches will provide you with the most part that you need to create a model of great applications.

Answer 2

Can I complement the excellent answer above with a link to the video:

http://sites.google.com/site/io/building-scalable-web-applications-with-google-app-engine

This is a great Google talk, Brett Slatkin, who talks for an hour about how you need to think about your application before you can expect it to scale well. There are some real WTFs (e.g. no count () in db queries) that will make you fight if you come from a relational background.

Answer 3

I think these are the basics: groups of keys and entities look for it in appengine docs. (I'm new here, so can't post the link)

Answer 4

I worked on this, but not an expert, although the Google engine for applications is very good, and this is the future because it implements the platform as a service and software as a service. The Google app engine provides a non-relational database. So, you are actually writing relationships here.

Regards, Gaurav J

Answer 5

These links are great, but python is prejudiced, I use GWT and so I have to use the java flavor of GAE, does anyone have any examples of how to achieve these “join” equivalents in the java version of GAE

Cheers, John

Answer 6

The standalone GAE SDK is quite difficult to use to enter data and retrieve data from the Google App Engine data warehouse.

"Objectify" is a GAE extension that simplifies these operations. Objectify wiki page and source code can be found here. I highly recommend using Objectify in your GAE project.

http://code.google.com/p/objectify-appengine/

Here are some guides on using Objectify with the application engine. Follow these tutorials and you'll instantly store and retrieve data.

http://www.fishbonecloud.com/2010/11/use-objectify-to-store-data-in-google.html